An IEEE (Institute of Electrical and Electronics Engineers) 802.16 standards provide techniques and protocols to support a broadband wireless access. Standardization proceeded starting from 1999 and IEEE 802.16-2001 was approved in 2001. It is based on a single carrier physical layer called ‘WirelessMAN-SC’. Later, besides the ‘WirelessMAN-SC’, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ were added to the physical layer in IEEE 802.16a standards approved in 2003. After the IEEE 802.16a standards were completed, revised IEEE 802.16-2004 standards were approved in 2004. IEEE 802.16-2004/Cor1 was completed in the form of ‘corrigendum’ in 2005 in order to resolve and correct bugs and errors of the IEEE 802.16-2004 standards.
One of systems considered in the next generation is an OFDM (Orthogonal Frequency Division Multiplexing) system that can attenuate an inter-symbol independent effect with a low complexity. The OFDM converts serially inputted data symbols into the N number of parallel data symbols, carries them in the N number of separated subcarriers, and transmits the same. The subcarriers maintain orthogonality in a frequency domain. The respective orthogonal channels experience mutually independent frequency selective fading, and the intervals of transmitted symbols are lengthened to minimize the inter-symbol interference. OFDMA refers to a multi-access scheme accomplishing multiple accesses by independently providing portions of available subcarriers to each user in a system using the OFDM as a modulation scheme. The OFDMA provides frequency resources called subcarriers to each user, and in general, the respective frequency resources are independently provided to multiple users so as not to overlap with each other. That is, resultantly, frequency resources are mutually exclusively allocated to the users.
A plurality of subcarriers provided to a user may be distributedly allocated to the overall frequency band for frequency diversity. Alternatively, a subcarrier of a particular frequency band may be locally allocated to a user with a good channel state in the corresponding frequency band. Currently, the IEEE 802.16 system employs TDM (Time Division Multiplexing in which a distributed allocation scheme and a local allocation scheme are discriminated by time domain. Namely, in the same time zone, distributed allocation and local allocation of subcarriers cannot be used together. Frequency resources are desired to be utilized according to each scheme suitable for various channel environments of multiple users, but the limitation in the allocation schemes of subcarriers according to time zones may restrict radio resource scheduling.
Thus, a method for freely using a subcarrier allocation scheme suitably according to various channel environments of users is required.